Optical sheeting formed of resin sheeting having a surface on which an array of micro optical elements that produce various optical effects are formed is used. Examples of such optical elements include cube corner prisms, linear prisms, lenticular lenses, refractive lenses, Fresnel lenses, linear Fresnel lenses, cross prisms, optical elements for holograms and planar optical elements.
In producing the optical sheeting, a highly accurate processing is required unlike common resin processing methods generally applied on surfaces of resin such as embossing, graining and satinizing since the geometric accuracy of the optical elements greatly affects the performance of the optical sheeting.
Patent Document 1 listed below discloses such an apparatus for producing optical sheeting and a method for producing optical sheeting. FIG. 11 is a diagram showing the apparatus for producing optical sheeting disclosed in Patent Document 1.
As shown in FIG. 11, the apparatus for producing optical sheeting includes, as main components: a pair of steel rolls 101 and 102 that rotate in the same direction; a circular belt mold 103 mounted around the pair of steel rolls 101 and 102; an extrusion die 104 that feeds synthetic resin sheeting; a rubber roll 107 that is pressed against the belt mold 103; and a rubber roll 108 that is pressed against the belt mold 103 between a position where the rubber roll 107 is pressed against the belt mold 103 and the steel roll 102.
The steel roll 101 has arranged therein heating means not shown in which heated oil circulates. On the other hand, the steel roll 102 has therein cooling means not shown which is cooled using a cooling medium. The steel rolls 101 and 102 rotate in the same direction at equal surface speeds.
The belt mold 103 mounted around the steel rolls 101 and  102 has a number of molds for an array of optical elements on a surface thereof, and turns unidirectionally around the steel roll 101 and the steel roll 102 with the rotation of the steel rolls 101 and 102. An area in which the belt mold 103 and the steel roll 101 are in contact with each other is a thermoforming zone.
The extrusion die 104 is attached to an extruder and feeds synthetic resin sheeting 105 onto the belt mold 103 at the thermoforming zone.
The rubber roll 107 presses the belt mold 103 in a state where a portion of the belt mold 103 onto which the synthetic resin sheeting 105 is fed from the extrusion die 104 is at the thermoforming zone. The pressing force is caused by a force applied to the rubber roll 107 by a hydraulic cylinder 106. Since the rubber roll 107 presses the belt mold 103 in this manner, the rubber roll 107 rotates at such a speed that the surface speed thereof is equal to the turning speed of the belt mold 103.
The rubber roll 108 is pressed against the belt mold 103 at a portion near an end point of the thermoforming zone by a force applied by an air cylinder 111 through a metallic arm  110 rotatably supported at a supported point thereof. The rubber roll 108 rotates at such a speed that the surface speed thereof is equal to the turning speed of the belt mold 103. Further, the rubber roll 108 is fed with carrier sheeting 109 from an unwinder 112.
A cooler 113 blowing air to the belt mold 103 is arranged between a position at which the belt mold 103 is pressed by the rubber roll 108 and a position at which the belt mold 103 is in contact with the steel roll 102. An area cooled by the cooler 113 and an area where the belt mold 103 and the steel roll 102 are in contact with each other constitute a cooling zone.
An optical device is produced as follows with such an apparatus for producing optical sheeting.
First, the synthetic resin sheeting 105 is continuously extruded through the extrusion die 104 onto the belt mold 103 at the thermoforming zone while the belt mold 103 is turning by the rotation of the steel rolls 101 and 102. The synthetic resin sheeting 105 extruded onto the belt mold 103 is then conveyed by the belt mold 103 to between the rubber roll 107 and the steel roll 101. The synthetic resin sheeting 105 is pressed by the rubber roll 107 and brought into intimate contact with the molds for an array of optical elements formed on the surface of the belt mold 103 to be in engagement with the belt mold 103. An array of optical elements is thus formed on one surface of the synthetic resin sheeting 105.
Then, the synthetic resin sheeting 105 in engagement with the belt mold 103 is moved together with the belt mold 103. Next, the synthetic resin sheeting 105 is moved near the end point of the thermoforming zone, where the synthetic resin sheeting 105 is fed with the carrier sheeting 109 on a surface opposite to the surface facing the belt mold 103 and is pressed by the rubber roll 108. The carrier sheeting 109 is thus laid on the surface of the synthetic resin sheeting 105. The formation of an array of optical elements is thus completed.
Next, the laminate of the synthetic resin sheeting 105 and the carrier sheeting 109 that travels together with the belt mold 105 is moved to the cooling zone, where it is cooled by the cooler 113 and further cooled by the steel roll 102 on the steel roll 102. The synthetic resin sheeting 105 is thus cooled to a temperature equal to or lower than the glass transition temperature of the synthetic resin forming the synthetic resin sheeting 105. The cooled laminate of the synthetic resin sheeting 105 and the carrier sheeting 109 is stripped from the belt mold 103 by means of a stripping roll  114 and wound up as a product (Patent Document 1).
In addition, Patent Document 2 listed below also discloses such an apparatus for producing optical sheeting and a method for producing optical sheeting. FIG. 12 is a diagram showing the apparatus for producing optical sheeting disclosed in Patent Document 2.
As shown in FIG. 12, the apparatus for producing optical sheeting includes, as main components: a pair of steel rolls  250 and 252; a circular belt mold 234 mounted around the steel rolls 250 and 252; a belt 282 configured to be pressed against the belt mold 234; and a plurality of auxiliary rolls 258 configured to press the belt 282 against the belt mold 234.
The belt mold 234 turns around the steel roll 250 and the steel roll 252 by the rotation of the steel rolls 250 and 252 in the same manner as the belt mold 103 disclosed in Patent Document 1 described above. Since the belt 282 is pressed against the belt mold 234 as described above, it turns around the auxiliary rolls 258 with the turning of the belt mold 234.
Sheets of Synthetic resin sheeting 212 and 242 pass between the belt molds 234 and the belt 282 so shat the synthetic resin sheeting 212 and the synthetic resin sheeting  242 are laminated into optical sheeting and engages with the belt mold 234. Subsequently, the optical sheeting is stripped from the belt mold 234 (Patent Document 2).